The Nasdaq composite slid 198 points, or 2.8 percent, to 6,989. The Russell 2000 index of small-company stocks gave up 26 points, or 1.8 percent, to 1,450.

The S&P 500 and Dow are now in the red for the year. The Nasdaq was holding on to a modest gain.

“We’re in a market where investors just want to sell any upside that they see,” said Lindsey Bell, investment strategist at CFRA. “The volatility we’ve seen the last couple of weeks has been pretty extreme in both directions.”

The benchmark S&P 500 was on track to cap a turbulent week of trading with its third weekly drop in four weeks. That would represent a big swing from just last week, when the index had its best weekly gain in nearly seven years.

Volatility has gripped the market since early October, reflecting investors’ worries that the Federal Reserve might overshoot with its campaign of rate increases and put the brakes on the U.S. economy.

Traders also fear that a prolonged trade dispute between the U.S. and China could slow the global economy and crimp corporate profits. Uncertainty over both those issues helped drive the market’s sell-off this week.

“The Fed has taken the punch bowl away in getting back to rates where they are today,” said Doug Cote, chief market strategist for Voya Investment Management. “We’re also going to get back to more normal volatility.”

Oil prices rose after OPEC countries agreed to reduce global oil production by 1.2 million barrels a day for six months, beginning in January. The move would include a reduction of 800,000 barrels per day from OPEC countries and 400,000 barrels per day from Russia and other non-OPEC nations.

The news, which had been widely anticipated, pushed crude oil prices higher. U.S. benchmark crude jumped 4.3 percent to $53.69 a barrel in New York. Brent crude, used to price international oils, gained 4.7 percent to $62.87 a barrel in London.

Tobacco company Altria Group, which makes Marlboro cigarettes, announced a $2.4 billion investment in Cronos Group, a Canadian medical and recreational marijuana company. Altria’ shares got a boost from the announcement, but the gain faded by late afternoon. The stock fell 0.2 percent to $54.28.

The Labor Department said U.S. employers added 155,000 jobs in November, a slowdown from recent months but enough to suggest that the economy is expanding at a solid pace despite sharp gyrations in the stock market. The unemployment rate remained at 3.7 percent, nearly a five-decade low, for the third straight month. Average hourly pay rose 3.1% from a year ago, matching the previous month’s figure, which was the best since 2009. The jobs figure was less than many economists forecast, but few saw the report as a sign of a broader slowdown.